1. Field of the Invention
The present invention relates to a glass antenna for vehicles, particularly to a glass antenna for receiving a digital TV broadcast formed on a rear glass. The present invention further relates to a glass antenna system using such a glass antenna.
2. Description of the Related Art
As a digital TV antenna for a vehicle, an antenna consisting of a pattern provided by a silver paste material formed on a glass window has been proposed as disclosed in Japanese Patent Publication Nos. 2002-135025 and 2003-124719.
In Japanese Patent Publication No. 2002-135025, there is disclosed that dedicated antennas for a digital TV broadcast are formed near the upper portions of a front glass and rear glass of a vehicle together with a reflector element and director element to control the directivity of the antenna, respectively.
In Japanese Patent Publication No. 2003-124719, there is disclosed a digital TV antenna which also serves as an antenna for other existed broadcasts, e.g., an analog TV broadcast.
As a slot antenna for a vehicle, an antenna has been proposed in which an electrical conductive film is coated on a front or rear window of a vehicle to form a slot between a vehicle body and the electrical conductive film as disclosed in Japanese Patent Publication Nos. 03-204202, 06-45817, and 09-175166.
It is difficult that a digital TV antenna having a good sensitivity is realized on a rear glass of a vehicle by the conventional antenna using silver printed lines. This is because a digital TV antenna of this type interferes with a plurality of (at most seven) other antennas of the same type provided in proximity to the digital TV antenna, resulting a low sensitivity thereof.
An antenna for existed broadcasts, e.g., an analog TV broadcast, may not be used as a dedicated antenna for a digital TV broadcast, because each of the existed broadcasts has a wide frequency range, resulting in the decrease of a sensitivity thereof.
In a case that a slot antenna is used, an electrical conducting transparent film is required to form a slot antenna on a glass window of a vehicle, because the peripheral portion of a slot antenna should be an electrical conducting material and the transparency of the glass window should not be disturbed.